System and method for calibrating a linear array using a calibration standard and a calibration piece with dark and light response measurements

A scanning system comprising:

• a linear array of a plurality of sensor chips, wherein each sensor chip of the plurality of sensor chips comprises a plurality of photosensors, at least one sensor chip of the plurality of sensor chips is a calibration sensor chip;
• a calibration standard positioned within a field of view of the calibration sensor chip;
• a processor arranged to execute a set of steps;
• and,
• a memory element arranged to store the set of steps comprising:
• exposing the plurality of sensor chips to an absence of illumination;
• measuring a dark response of each photosensor of the plurality of photosensors;
• positioning a calibration piece within a field of view of the plurality of sensor chips other than the calibration sensor chip;
• illuminating the calibration standard and the calibration piece with a light source;
• measuring a light response of each photosensor of the plurality of photosensors;
• applying an offset to the light response of each photosensor of the plurality of photosensors by subtracting the dark response of each photosensor of the plurality of photosensors to obtain an offset light response for each photosensor of the plurality of photosensors;
• calculating a mean offset light response for each sensor chip of the plurality of sensor chips by averaging the offset light response for each photosensor of the plurality of photosensors in each sensor chip of the plurality of sensor chips;
• calculating a modified light response for each photosensor of the plurality of photosensors by modifying the offset light response for each photosensor of the plurality of photosensors based on the mean offset light response of the sensor chip comprising the respective photosensor, the mean offset light response of the calibration sensor chip, an initial mean offset light response of the sensor chip comprising the respective photosensor, and an initial mean offset light response of the calibration sensor chip;
• and,
• applying a first gain to the offset light response of each photosensor of the plurality of photosensors based on the modified light response of each respective photosensor to obtain a corrected light response of each photosensor of the plurality of photosensors.

A method of balancing responses of a plurality of sensor chips arranged generally in a linear array, wherein each sensor chip of the plurality of sensor chips comprises a plurality of photosensors, at least two sensor chips of the plurality of sensor chips are a calibration sensor chip and a calibration standard is positioned within a field of view of the calibration sensor chips, the method comprising:

• exposing the plurality of sensor chips to an absence of illumination;
• measuring a dark response of each photosensor of the plurality of photosensors;
• positioning a calibration piece within a field of view of the plurality of sensor chips other than the calibration sensor chips;
• illuminating the calibration standard and the calibration piece with a light source;
• measuring a light response of each photosensor of the plurality of photosensors;
• applying an offset to the light response of each photosensor of the plurality of photosensors by subtracting the dark response of each photosensor of the plurality of photosensors to obtain an offset light response for each photosensor of the plurality of photosensors;
• calculating a mean offset light response for each sensor chip of the plurality of sensor chips by averaging the offset light response for each photosensor of the plurality of photosensors in each sensor chip of the plurality of sensor chips;
• calculating a first gain according to the following equation:
• g
• ⁢
• ⁢
• 1
• =
• [
• R_calibration
• ⁢
• _sensors
• R
• _
• -
• (
• R_calibration
• ⁢
• _sensor
• 0
• _
• -
• R_non
• ⁢
• _calibration
• ⁢
• _sensors
• 0
• _
• )
• ]
• R_non
• ⁢
• _calibration
• ⁢
• _sensors
• R
• ,
• where:
• g1 is the first gain,
• R_calibration_sensorsR is an average of the mean offset light responses of each of the calibration sensor chips,
• R_calibration_sensors0 is an average of the initial mean offset light responses of each of the calibration sensor chips,
• R_non_calibration_sensorsR is an average of the mean offset light response of each of the plurality of sensor chips other than the calibration sensor ship, and
• R_non_calibration_sensors0 is an average of the initial mean offset light response of each of the plurality of sensor chips other than the calibration sensor ship;
• and,
• multiplying the first gain by the offset light response for each photosensor of the plurality of photosensors for each sensor chip of the plurality of sensor chips to obtain the modified light response of each photosensor of the plurality of photosensors.
• applying a second gain to the offset light response of each photosensor of the plurality of photosensors based on the modified light response of each respective photosensor to obtain a corrected light response of each photosensor of the plurality of photosensors.